System for exhaust gas treatment for internal combustion engines

ABSTRACT

A System for exhaust gas treatment for internal combustion engines, having a pump ( 1 ) for metered supply of a freezable substance, particularly a urea solution, to a supply device ( 23 ) introducing said substance into the exhaust gas flow, is characterised in that a compensation device ( 25 ) is provided as protection against damage to the System due to volume expansion when the substance freezes, said compensation device compensating for the volume expansion accompanying an increase of the fluid pressure when the substance freezes.

The invention relates to a system for exhaust gas treatment for internalcombustion engines, comprising a pump for a metered supply of afreezable substance, in particular an aqueous urea solution, to a supplydevice introducing said substance into the exhaust gas flow.

Such systems, which are also referred to in technical language as theAdblue system, can be used in automotive engineering to reduce nitrogenoxides contained in the exhaust gas flow to nitrogen. This takes placeby means of the metered supply of an aqueous urea solution from a supplytank, via a supply device, to the exhaust gas flow, wherein ammonia isobtained from the urea by hydrolysis. The ammonia functions as aselective reducing agent in the exhaust gas flow. In order to optimizethe efficiency of the reduction, the aqueous urea solution is suppliedto the exhaust gas flow in a metered manner by means of a pump, which iscontrolled by a control device in a load-dependent manner.

The water content of the urea solution, which functions as an additionalworking substance, has a disadvantageous effect on the operatingbehavior. If the aqueous solution should freeze, the entire system couldfail, in particular as a result of the pump and the supply deviceconnected thereto becoming damaged or destroyed. This risk exists, inparticular, during immobilization times at frost temperatures.

In light of these issues, the problem addressed by the invention is thatof providing an Adblue system in which the risk of damage due to theeffects of frost is minimized.

According to the invention, this problem is solved by a system havingthe features of claim 1 in totality.

According to the characterizing part of claim 1, an essential specialfeature of the invention is that a compensation device is provided asprotection against damage to the system due to volume expansion when thesubstance freezes, said compensation device compensating for the volumeexpansion accompanying an increase of the fluid pressure when thesubstance freezes. The risk that would exist otherwise is therebyavoided, namely that, if an aqueous substance freezes, as is the casewith an aqueous urea solution under frost conditions, the resultantincrease in volume causes walls to burst or, in particular, damages ordestroys the pump and/or the valve devices that belong thereto.

In a particularly advantageous manner, the compensation device cancomprise at least one component that is connected to the fluid chamberof the system and that has predetermined resilience that enables thefluid chamber to enlarge in a pressure-dependent manner.

In order to provide such resilience, in the case of exemplaryembodiments comprising a displacement-type pump having at least onedisplacement element that can be moved by an actuator, the arrangementcan be advantageously designed such that the displacement elementinteracts with the actuator via a resilient coupling device that permitsa pressure-dependent relative motion to take place.

In particularly advantageous exemplary embodiments, a piston pumpcomprising at least one pump piston can be provided, wherein thecoupling device has a compression spring, which is installed between therespective pump piston and the actuator and allows the piston to move,against the spring force of said compression spring and relative to theactuator, such that the fluid chamber is enlarged.

Particularly advantageously, the actuator can be formed by an actuatingpart of a magnet piston, which can move axially in the pole tube of asolenoid device.

In particularly advantageous exemplary embodiments, the pump piston canbe lengthened, on the side facing away from the fluid chamber, by asleeve part that is guided in the pump cylinder and is open toward theactuating part of the magnet piston, wherein the compression spring isdisposed in the interior space of the sleeve part. Due to the fact thatthe lengthened piston guide is used simultaneously as the springhousing, a compact design of the pump can be obtained.

In an advantageous manner, the solenoid device can be designed as apressing magnet, which, when current flows through the magnet coil,presses the magnet piston, together with the actuating part, against thecompression spring and moves the pump piston for a delivery stroke.

The arrangement is preferably designed such that, when current is notsupplied to the magnet coil, a return spring acts on the pump piston andmoves said pump piston for a return stroke.

In order to preload the actuating part of the magnet piston against thecompression spring in a force-locking manner when current is notsupplied to the magnet coil, a spring that acts counter to the returnspring can act on the magnet piston, wherein the spring force of thisspring is less than that of the return spring.

In particularly advantageous exemplary embodiments, a magnet coil thatheats up when supplied with current is provided as a heat source, whichfunctions as freeze protection and as a thawing device via a thermalcoupling to the pump. It is thereby made possible in a particularlyadvantageous manner that, when a cold start of the internal combustionengine is attempted under frost conditions, with the urea solutionfrozen and, therefore, the pump blocked, the cold-running phase, inwhich exhaust gas treatment does not take place, lasts only for as longas it takes for the pump to be automatically thawed out by the heat ofthe magnet coil so that said pump can begin operating and exhaust gastreatment can begin. It is also ensured by means of the heat provided bythe magnet coil that, in the event that the ambient temperature dropsinto the frost range during operation, the pump is prevented fromfreezing and the failure of the exhaust gas treatment that would resultis also prevented.

The invention is explained in detail in the following by reference toexemplary embodiments illustrated in the drawings. Therein:

FIG. 1 shows a longitudinal view only of the region of an exemplaryembodiment of the system according to the invention that is adjacent tothe pump, wherein said longitudinal view is enlarged and cut off withrespect to a practical embodiment;

FIG. 2 shows a cut-off subsection of the region adjacent to the pump,which is shown on a smaller scale than in FIG. 1 and is rotated by 90°relative thereto, wherein a filter device allocated thereto is merelyindicated, in an incomplete depiction;

FIG. 3 shows a depiction of a modified exemplary embodimentcorresponding to FIG. 2;

FIG. 4 shows a longitudinal view of only the filter device for theexemplary embodiments of the system according to the invention, in aschematically simplified illustration, and

FIG. 5 shows an enlarged, schematically simplified and cut-offsubsection only of the region of a further exemplary embodiment of thesystem according to the invention that is adjacent to an end region ofthe filter device and comprises sensors.

Proceeding from an exemplary embodiment of the system according to theinvention, FIG. 1 shows a pump 1 as a component of a supply device,which extends from a non-illustrated supply tank containing a supply ofan aqueous urea solution, via the pump 1 to a filter device, which isbest shown in FIG. 4, and, from said filter device, to an injectionnozzle (likewise not illustrated), which sprays a metered amount of theurea solution into the exhaust gas stream. In addition, a further pumpor another type of delivery system that increases the pressure to thefinal injection pressure can be provided. The urea solution reaches thepump 1 via an inlet line 3, wherein said pump delivers a metered amountof the urea solution from the pump outlet 5 to the filter inlet 7 of thefilter device 9, which is depicted in greater detail in FIG. 4. As isclear from FIGS. 2 and 3, the pump 1 is designed as a piston pump, thecylinder 11 of which is visible in FIGS. 2 and 3 and, in each case, isrotated 90° relative to the plane of the drawing of FIG. 1. As shown inFIG. 1, a non-return valve 13 and 15, respectively, having spring-loadedclosing bodies 17 and 19, respectively, are located at the inlet line 3and at the outlet 5 of the pump 1, wherein the non-return valve 13 opensduring the intake stroke of the pump 1 and the non-return valve 15closes during the delivery stroke of the pump 1. Sealing rings 21 formthe seal at the non-return valves 13, 15. The urea solution emergingfrom the filter device 9 reaches the exhaust gas stream via an outletline 23.

As mentioned previously, the pump 1 is a piston pump. The pump piston25, which is guided in the cylinder 11, is lengthened at the end thereoffacing away from the fluid chamber 27 of the pump 1 by a sleeve part 29,by means of which the piston 25 is guided in an axially movable mannerat the wall of the cylinder 11, wherein a piston seal 31 is provided forsealing. The inner space 33 of the sleeve part 29 is open at the endopposite the fluid chamber 27. A compression spring 35 is inserted intothe inner space 33 from the open end. This compression spring issupported on one side at the closed base of the sleeve part 29 and, onthe other side, at a thrust element 37, which is displaceable in thesleeve part 29 at the open end of said sleeve part. As an alternative,the thrust element could also be disposed on the inside, although saidthrust element would then have to be sealed off from this inner space,for example by means of an O ring.

An actuating part 39 interacts with the free side of the thrust element37, said actuating part being formed by an extension of a magnet piston41. This actuating part 39 is displaceably guided in a pole body 43 of asolenoid device 45. The pole body 43 transitions into a pole tube 49 viaa tapering point 47 having a reduced material cross section, which formsa magnetic gap, wherein the magnet piston 41, which is connected to theactuating part 39, can move in the mentioned pole body. The magnet coil51, which can be supplied with current via a connecting device 53, islocated in a ferromagnetic magnet housing 55 having a pole plate 57. Thesolenoid device 45 is designed as a so-called “pressing” magnet,wherein, when current is supplied to the magnet coil 51, the magnetpiston 41 presses the actuating part 39 against the thrust element 37and therefore presses the compression spring 35. As a result, the pumppiston 25 is moved via the compression spring 35 to the left, as shownin the drawing, for a delivery stroke, by means of which a dosed amountof the urea solution is dispensed from the fluid chamber 27 via thenon-return valve 15 at the pump outlet 5. FIGS. 2 and 3 each show thecurrentless state of the solenoid device 45. When current is supplied tothe coil 51, the actuating part 39 moves the piston 25, for a deliverystroke, to the left as shown in the drawing against the force of areturn spring 59, which is located in the fluid chamber 27, and, whenthe current supply to the coil 51 is halted, said actuating part movesthe pump piston 25 back toward the right, into the starting positionshown in FIGS. 2 and 3. In the exemplary embodiment of FIG. 2, the freeend of the magnet piston 41 rests against an end stop, which is formedby a terminating element 61 at the end of the pole tube 49.

The pump piston 25 can perform a reciprocating motion even when themagnet piston 41 is located in an end position, as shown in FIG. 2,where further motion of the actuating part 39 is blocked in a directionthat corresponds to the enlargement of the volume of the fluid chamber27, because the compression spring 35 is a resilient component that canbe compressed when the pressure increase in the fluid chamber 27 isexcessive, thereby enabling the pump piston 25 to make a motion to theright as shown in the drawing, which enlarges the volume of the fluidchamber 27, wherein the end 63 of the sleeve part 29 moves into a freespace 65 at the pole body 43. Due to the thusly formed resilience, it ispossible to safely compensate for the increase in volume that occurswhen the urea solution freezes in the fluid chamber 27. A diaphragm seal67, as an additional sealing element, is located in the free space 65.

FIG. 3 shows a variant in which an additional spring 69 is providedinstead of the fixed end stop of the magnet piston 41, which is formedby the end piece 61, wherein said additional spring constantly holds theactuating part 39 of the magnet piston 41 against the thrust element 37of the compression spring 35 in a force-locking manner, but has a weakerspring effect than the return spring 59.

FIG. 4 shows additional details of the filter device 9, which comprisesa filter housing 71 in the form of a circular cylindrical pot having aclosed base 73. The housing 71 is closed at the open end by means of anend cap 75 of a filter element 77, which is accommodated in the housing71. The filter element 77 comprises a hollow cylindrical filter medium81, which surrounds an inner filter cavity 79, wherein the inner side ofsaid filter medium rests against a support tube 83 and is enclosed onthe outer side by a support body 85. Within the filter housing 71, thementioned support body delimits a partial volume that delimits the fluidchamber as a partial volume of the housing 71 that is in fluidicconnection with the inner filter cavity 79. The inlet (filter inlet 7 ofFIGS. 2 and 3) and the outlet 90 of the fluid chamber of the filterhousing 71 are located at the end cap 75 of the filter element 77. Anelectric heating rod 87 extends through a central opening 86 of the endcap 75 and into the inner filter cavity 79. For the purpose of thermalcoupling with the heating rod 87, a metallic filler piece 89 adjoinssaid heating rod at the end thereof.

In order to allow the partial volume to enlarge relative to theremaining volume in the filter housing 71 when the aqueous urea solutionfreezes in said partial volume, which forms the fluid chamber, a casing91 made of a material having a predefined compressibility is provided asa resilient element between the inner wall of the housing 71 and theouter side of the filter element 77. In the present exemplaryembodiment, a casing 91 made of microcellular rubber is provided forthis purpose and, in the example shown, completely surrounds the filterelement 77, proceeding from the end cap 75. The casing 91 thereforefills all the residual volume within the filter housing 71, wherein saidresidual volume decreases relative to the partial volume that forms thefluid chamber when the casing 91 is compressed in order to allow thepartial volume formed by the fluid chamber to safely increase when theurea solution freezes in the fluid chamber.

FIG. 5 shows, in an exemplary embodiment of the system according to theinvention, the connecting piece 92 comprising the inlet line 3, whichleads to the pump 1, and the outlet line 23 for the metered delivery ofthe urea solution. A temperature sensor 93 and a pressure sensor 94 areconnected to the outlet line 23. Each of the FIGS. 2 to 4 show plug caps96 on the electric plug connection 95 of the sensors 93, 94, while FIG.5 shows a plug cap 96 on only the pressure sensor 94. Both sensors 93,94 are embodied as screw-in sensors and are screwed into the connectingpiece 92 by means of screw-in threads 97 and 98. The measurement probe99 of the temperature sensor 93 thereby extends into the outlet line 23.A pressure-transferring element, for example in the form of a diaphragm88, is fluidically connected to the outlet line 23 on the side havingthe pressure sensor 94.

A resilient component is assigned to each sensor 93 and 94 as freezeprotection, wherein said resilient component forms a resilient wall partat the fluid region of the respective sensor 93, 94. To this end, in thecase of the temperature sensor 93, a resilient cushion 100, which is inthe form of a cube made of microcellular rubber in the present example,is provided at the part of the outlet line 23 opposite the measurementprobe 99. On the side having the pressure sensor 94, a cushion 101 inthe form of a plate is disposed at a corresponding point of the outletline 23, wherein said plate is also made of microcellular rubber andalso forms a resilient wall part of the outlet line 23 at the inletregion of the sensor 94. Due to this resilience, it is possible tocompensate for the increase in volume that results when the aqueous ureasolution freezes in the outlet line 23, thereby preventing damage to theconnecting regions of the sensors 93, 94, such as the measurement probe99 and the screw-in thread 97, 98.

It is understood that, instead of a compressible body, such as themicrocellular-rubber cushion, a resilient wall part could be provided atthe outlet line 23 or at the sensor 93, 94, such as a component that issupported by a spring element, as shown in FIGS. 2 and 3.

1. A system for exhaust gas treatment for an internal combustion engine,comprising at least one pump (1) for a metered supply of a freezablesubstance, in particular in the form of an aqueous urea solution, to asupply device (23) introducing said substance into the exhaust gas flow,wherein parts of the pump (1) interact with at least one fluid chamber(27) for the at least temporary accommodation of the freezablesubstance, characterized in that, as protection against damage to thesystem due to volume expansion when the substance freezes, acompensation device (25) acts on the respective fluid chamber (27) suchthat a volume expansion accompanying an increase of the fluid pressurewhen the substance freezes is compensated for within the assignablefluid chamber (27).
 2. The system according to claim 1, characterized inthat the compensation device comprises at least one component (25) thatis connected to the fluid chamber (27) of the system and haspredetermined resilience that enables the fluid chamber (27) to enlargein a pressure-dependent manner.
 3. The system according to claim 1,characterized in that a pump (1) that is of the displacement type andhas at least one displacement element (25) that can be moved by anactuator (39, 41) is provided as a component, and in that saidcomponent, as a component of the compensation device, interacts with theactuator (39, 41) via a resilient coupling device (35, 37) that permitsa pressure-dependent relative motion to take place.
 4. The systemaccording to claim 1, characterized in that a piston pump comprising atleast one pump piston (25) is provided, and in that the coupling device(35, 37) has a compression spring (35), which is tensioned between therespective pump piston (25) and the actuator (39, 41) and allows thepump piston (25) to move, against the spring force and relative to theactuator (39, 41), such that the fluid chamber (27) enlarges.
 5. Thesystem according to claim 1, characterized in that the actuator isformed by an actuating part (39) of a magnet piston (41), which can moveaxially in the pole tube (49) of a solenoid device (45).
 6. The systemaccording to claim 1, characterized in that the pump piston (25) islengthened, on the side facing away from the fluid chamber (27), by asleeve part (29) that is guided in the pump cylinder (11) and is opentoward the actuating part (39) of the magnet piston (41), and in thatthe compression spring (35) is disposed in the interior space (33) ofthe sleeve part (29).
 7. The system according to claim 1, characterizedin that the solenoid device (45) is designed as a pressing magnet,which, when current flows through the magnet coil (51), presses themagnet piston (41), together with the actuating part, against thecompression spring (35) and moves the pump piston (25) for a deliverystroke.
 8. The system according claim 1, characterized in that, whencurrent is not supplied to the magnet coil (51), a return spring (59)acts on the pump piston (25) and moves said pump piston for a returnstroke.
 9. The system according claim 1, characterized in that a spring(69) is provided on the magnet piston (41) that preloads the actuatingpart (39) against the compression spring (35) in a force-locking mannerwhen current is not supplied to the magnet coil (51) and acts counter tothe force of the return spring (59).
 10. The system according to claim1, characterized in that a magnet coil (51) that heats up when suppliedwith current is provided as a heat source, which functions as freezeprotection and as a thawing device via a thermal coupling to the pump(1).
 11. The system according claim 1, characterized in that the supplydevice (23) comprises at least one filter device (9) having a filter forthe filtration of the freezable substance.
 12. The system accordingclaim 1, characterized in that the compensation device comprises atleast one resilient element (91) in the housing (71) of the filterdevice (9), which permits a pressure-dependent enlargement of the volumeof the fluid chamber (79) interacting with the filter device (9). 13.The system according claim 1, characterized in that the supply device(23) comprises at least one sensor device having sensors (93, 94), whichdetect state variables associated with the freezable substance, such aspressure and temperature.
 14. The system according to claim 1,characterized in that parts (100, 101) of the sensor device interactwith at least one fluid chamber (23) for the at least temporaryaccommodation of the freezable substance, and in that the compensationdevice comprises at least one resilient element (100, 101), whichpermits a pressure-dependent enlargement of the fluid chamber (23).